1. Field of Invention
The invention relates generally to control apparatus and methods for a multi-cylinder internal combustion engine.
2. Description of Related Art
Conventionally, a control apparatus for a multi-cylinder internal combustion engine, which reduces variation in the air-fuel ratio between cylinders is known. An example of this type of control apparatus is disclosed in Japanese Patent Application Laid-Open Publication No. 6-213044. The control apparatus disclosed in this publication calculates the air-fuel ratio of each of a plurality of cylinders based on a value output from an air-fuel sensor. Any variation in the air-fuel ratios between the cylinders is then minimized by controlling the valve lift amount of each of the cylinders.
Variation in the fuel injection quantity between cylinders, however, may lead to a variation in torque between the cylinders, which may result in pulsation. With the control apparatus disclosed in the above-mentioned publication, it is possible that, even if a variation in air-fuel ratio between the cylinders is minimized, a variation in torque may still occur between the cylinders.
Further in the control apparatus disclosed in the foregoing publication, although variation in the air-fuel ratio between the cylinders is minimized by controlling the valve lift amount, the publication discloses nothing about how to control the variation in air-fuel ratio between the cylinders in the event that the amount of valve overlap of the intake valve and the exhaust valve can be changed. Moreover, the publication discloses nothing about how to control the variation in the air-fuel ratio between the cylinders in the event that the operation angle of the intake valve can be changed. Therefore, variation in the air-fuel ratio between the cylinders with this control apparatus is not able to be appropriately controlled both in the case where the amount of the valve overlap of the intake valve and the exhaust valve is able to be changed, and in the case where the operation angle of the intake valve is able to be changed.